Stable quantum bits, capable both of storing quantum information for macroscopic time scales and of integration inside small portable devices, are an essential building block for an array of potential applications. The realization of such stable quantum bits represents an outstanding challenge at the interface of quantum science and engineering. Such qubits are the essential building blocks for an array of potential applications in quantum communication and computation, many of which rely on the ability to maintain qubit coherence for extended periods of time.
Integrating such quantum-mechanical systems in compact mobile devices remains an outstanding experimental task. For a majority of quantum systems, lifetimes are limited to a tiny fraction of a second due to external perturbations and decoherence. Although trapped ions and atoms can exhibit coherence times as long as minutes, they typically require a complex infrastructure involving laser cooling and ultrahigh vacuum. Other systems, most notably ensembles of electronic and nuclear spins, have also achieved long coherence times in bulk electron spin resonance (ESR) and nuclear magnetic resonance (NMR) experiments.
For single spins or qubits, however, individual preparation, addressing, and high-fidelity measurement remain challenging, even at cryogenic temperatures, owing to their exceptional isolation.